:root {
  --bg: #f4f5fa;
  --card: #ffffff;
  --ink: #1b1e32;
  --muted: #6b7280;
  --line: #e3e6f0;
  --accent: #4f46e5;
  --accent-soft: #eef2ff;
  --good: #16a34a;
  --good-soft: #f0fdf4;
  --bad: #dc2626;
  --bad-soft: #fef2f2;
  --unknown: #d97706;
  --unknown-soft: #fffbeb;
  --radius: 14px;
}

* { box-sizing: border-box; -webkit-tap-highlight-color: transparent; }

html, body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: ui-sans-serif, system-ui, -apple-system, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  font-size: 16px;
  line-height: 1.5;
}

.container { max-width: 640px; margin: 0 auto; padding: 16px; }

.hidden { display: none !important; }

/* header */
#header {
  position: sticky; top: 0; z-index: 20;
  background: rgba(255,255,255,0.92);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--line);
}
.header-inner { display: flex; align-items: center; gap: 10px; padding-top: 10px; padding-bottom: 10px; }
.brand { font-weight: 800; font-size: 18px; letter-spacing: -0.02em; text-decoration: none; color: inherit; cursor: pointer; }
.header-user { flex: 1; text-align: right; color: var(--muted); font-size: 14px; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.link-btn { background: none; border: none; color: var(--accent); font-size: 14px; font-weight: 600; cursor: pointer; padding: 6px 8px; border-radius: 8px; }
.link-btn:hover { background: var(--accent-soft); }

/* cards & type */
.card {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 18px;
  margin-bottom: 14px;
  box-shadow: 0 1px 2px rgba(20, 24, 60, 0.04);
}
h1 { font-size: 22px; margin: 0 0 6px; letter-spacing: -0.02em; }
h2 { font-size: 18px; margin: 0 0 10px; letter-spacing: -0.01em; }
p { margin: 0 0 10px; }
.muted { color: var(--muted); }
.small { font-size: 13px; }
.center { text-align: center; }

/* buttons */
.btn {
  display: block; width: 100%;
  background: var(--accent); color: #fff;
  border: none; border-radius: 12px;
  padding: 14px 16px; font-size: 16px; font-weight: 700;
  cursor: pointer; margin-top: 10px;
  min-height: 48px;
}
.btn:hover { filter: brightness(1.06); }
.btn:disabled { opacity: 0.5; cursor: default; filter: none; }
.btn.secondary { background: var(--accent-soft); color: var(--accent); }
.btn.ghost { background: transparent; color: var(--accent); border: 1.5px solid var(--accent); }

/* option buttons (answers) */
.opt {
  display: flex; align-items: flex-start; gap: 10px;
  width: 100%; text-align: left;
  background: var(--card); color: var(--ink);
  border: 1.5px solid var(--line); border-radius: 12px;
  padding: 13px 14px; font-size: 15.5px; line-height: 1.45;
  cursor: pointer; margin-bottom: 10px; min-height: 48px;
  transition: border-color 0.12s, background 0.12s;
}
.opt:hover { border-color: var(--accent); }
.opt .letter {
  flex: 0 0 auto; width: 26px; height: 26px; border-radius: 50%;
  background: var(--accent-soft); color: var(--accent);
  font-size: 13px; font-weight: 800;
  display: flex; align-items: center; justify-content: center;
  margin-top: 1px;
}
.opt:disabled { cursor: default; }
.opt.correct { border-color: var(--good); background: var(--good-soft); }
.opt.correct .letter { background: var(--good); color: #fff; }
.opt.wrong { border-color: var(--bad); background: var(--bad-soft); }
.opt.wrong .letter { background: var(--bad); color: #fff; }
.opt.unknown-opt { border-style: dashed; border-color: var(--unknown); color: var(--unknown); background: var(--unknown-soft); }
.opt.unknown-opt .letter { background: var(--unknown); color: #fff; }

/* feedback */
.feedback { border-radius: 12px; padding: 12px 14px; margin: 4px 0 12px; font-weight: 700; font-size: 15px; }
.feedback.good { background: var(--good-soft); color: var(--good); }
.feedback.bad { background: var(--bad-soft); color: var(--bad); }
.feedback.unknown { background: var(--unknown-soft); color: var(--unknown); }

/* explainer */
.explainer { border-left: 3px solid var(--accent); background: var(--accent-soft); border-radius: 0 12px 12px 0; padding: 12px 14px; margin-top: 12px; }
.explainer h3 { margin: 0 0 6px; font-size: 14px; text-transform: uppercase; letter-spacing: 0.05em; color: var(--accent); }
.explainer p { margin: 0 0 8px; font-size: 14.5px; }
.explainer p:last-child { margin-bottom: 0; }

/* chips */
.chips { display: flex; flex-wrap: wrap; gap: 6px; margin: 8px 0 4px; }
.chip {
  font-size: 12px; font-weight: 700; padding: 3px 9px; border-radius: 999px;
  background: var(--accent-soft); color: var(--accent);
}
.chip.subject { background: #e0e7ff; }
.chip.cat { background: #f3f4f6; color: var(--muted); }
.chip.diff-easy { background: var(--good-soft); color: var(--good); }
.chip.diff-medium { background: var(--unknown-soft); color: var(--unknown); }
.chip.diff-hard { background: var(--bad-soft); color: var(--bad); }
.chip.filter { cursor: pointer; padding: 6px 12px; border: 1.5px solid var(--line); background: #fff; color: var(--muted); }
.chip.filter.active { background: var(--accent); border-color: var(--accent); color: #fff; }

/* progress */
.progress-track { height: 8px; background: var(--line); border-radius: 999px; overflow: hidden; margin: 10px 0 16px; }
.progress-fill { height: 100%; background: var(--accent); border-radius: 999px; transition: width 0.25s; }

/* subject bars (results) */
.subject-row { margin-bottom: 14px; }
.subject-row .top { display: flex; justify-content: space-between; align-items: baseline; margin-bottom: 4px; }
.subject-row .name { font-weight: 700; font-size: 15px; }
.subject-row .stat { font-size: 13px; color: var(--muted); }
.bar-track { height: 10px; background: var(--line); border-radius: 999px; overflow: hidden; }
.bar-fill { height: 100%; border-radius: 999px; background: var(--accent); }
.bar-fill.low { background: var(--bad); }
.bar-fill.mid { background: var(--unknown); }
.bar-fill.high { background: var(--good); }

/* review cards */
.review-card .q { font-size: 15px; font-weight: 600; margin-bottom: 8px; }
.review-opt { display: flex; gap: 8px; font-size: 14px; padding: 8px 10px; border-radius: 10px; margin-bottom: 6px; background: #f8f9fc; }
.review-opt.correct { background: var(--good-soft); }
.review-opt.wrong { background: var(--bad-soft); }
.review-opt .mark { font-weight: 800; }

/* misc */
.grid-2 { display: grid; grid-template-columns: 1fr 1fr; gap: 10px; }
.field { width: 100%; padding: 13px 14px; font-size: 16px; border: 1.5px solid var(--line); border-radius: 12px; margin-bottom: 10px; background: #fff; }
.field:focus { outline: none; border-color: var(--accent); }
.error { color: var(--bad); font-size: 14px; font-weight: 600; margin: 6px 0; }
.big-score { font-size: 52px; font-weight: 800; letter-spacing: -0.03em; line-height: 1; }
.rank-list { margin: 8px 0 0; padding-left: 20px; }
.rank-list li { margin-bottom: 6px; font-size: 15px; }
.toast {
  position: fixed; left: 50%; bottom: 24px; transform: translateX(-50%);
  background: var(--ink); color: #fff; padding: 12px 18px; border-radius: 12px;
  font-size: 14px; font-weight: 600; z-index: 50; box-shadow: 0 6px 20px rgba(0,0,0,0.2);
  max-width: 90vw; text-align: center;
}
.auth-tabs { display: flex; gap: 8px; margin-bottom: 14px; }
.auth-tabs .btn { margin-top: 0; }
.divider { height: 1px; background: var(--line); margin: 14px 0; }